The invention relates to telecommunication systems and especially to a method and equipment for implementing call forwarding in a mobile system comprising at least one forwarding exchange for carrying out call forwarding on the basis of subscriber data related to the call forwarding, and at least one subscriber database for storing the subscriber data related to the call forwarding. The method comprises the steps of receiving at the forwarding exchange a call addressed to a subscriber in the mobile system, performing a subscriber data request to the subscriber database, and transmitting a response message from the subscriber database to the forwarding exchange, the message containing data indicating the call forwarding and a forwarding number.
Modern mobile systems provide subscribers with different data transmission properties in addition to conventional speech transmission. Mobile system services can be divided generally into teleservices and bearer services. A bearer service is a telecommunication service that constitutes the transmission of signals between user-network interfaces. For example modem services are bearer services. In a teleservice, the network also provides terminal services. Important teleservices in turn include speech, facsimile and videotex services.
One mobile subscriber may typically have access to different tele- and bearer services that are referred to in this connection as basic services. A subscriber may use for example a speech, facsimile and data service. A call terminating at or originating from a mobile station may therefore require any of these basic services, and therefore the correct service must be indicated to the mobile network. For example in a GSM mobile system, call set-up signalling transmitted by a mobile station contains data about the required basic service in a bearer capability information element (BCIE). In this manner, the mobile network is able to select the correct basic service for calls originating from the mobile station. Calls arriving from an integrated services data network (ISDN) also contain a corresponding information element that indicates the required service. However, if the call arrives from a public switched telephone network (PSTN) or travels through it, the mobile network does not receive such data concerning the service type of the call. In such a case, the mobile network should know in some other manner the type of basic service required by the call.
A known solution to this problem is a multi numbering scheme, here a mobile subscriber has as many numbers as he has services to which he wants to receive incoming calls. The number is also called the mobile subscriber ISDN number, i.e. MSISDN. For example, a subscriber may have a number for a speech service, a facsimile service and a modem service. In a multi numbering scheme, the calling subscriber selects from the mobile subscriber's numbers the one corresponding to the desired service.
An additional service in mobile systems is call forwarding that may be activated by a subscriber. Call forwarding may be unconditional, in which case a call is always transferred to the new number given. Call forwarding may also be set to be conditional, for example when the subscriber is busy, does not respond or cannot be reached. Due to the multi numbering scheme, the subscriber may transfer different types of calls addressed to him to different numbers. However, this requires that the subscriber determines the basic service to which the forwarding is directed in connection with the activation of the forwarding. If no basic service is determined, all subscriber calls are transferred to the same number. When the subscriber determines the forwarding specifically for each basic service, he has to activate the forwarding several times and to manage separately the set of numbers related to each service, the activated forwarding procedures etc. The management of such functions requires that the users are well trained, which consumes resources. There is also the danger that functions that are found to be difficult are not used.
One of the most common forms of call forwarding is the voice mail service where a subscriber directs the received calls to be transferred, either unconditionally or conditionally, to a voice mail service centre (VMS) that attends to responding to the calls and that stores the messages left for the subscriber. Most VMSs are capable of distinguishing whether an incoming call is a speech call or a facsimile call, but this requires that for each call arriving at the VMS there is an equipment that identifies the incoming call type. The number and costs of the equipments required could be reduced considerably if different types of incoming calls would be directed to the exchange via different lines. In order for the calls to be transferred to the VMS, the called party number Cd# must be the same in the forwarding and therefore different types of calls cannot be distinguished from one another on the basis of analysing the called party number.